Safety device for vacuum tubes



Filed July 17 1919 A MUTSCHELLER SAFETY DEVICE FOR VACUUM TUBES wventoz ,4m-Hw? Murau/cue@ Patented Feb. 12, 1924.

UNITED STATES PATENT OFFICE.

ARTHUR MUTSCHELLR, OF NEW YORK, N. Y., V,ASSIGNOR TO WAPPLER ELECTRIC COM- PANY, INC.,v A. CORPORATION OF NEW YORK.

SAFETY DEVICE FOR VACUH TUBES.

Application led July 17, 1919. Serial No. 811,518.

To all 'whom it may concern Be it known that I, ARTHUR MUTscHnL- LER. a cit-izen of the United States, residing at New York, county of New York, and

State of New York, have invented certain new and useful Improvements in Safety Devices for Vacuum Tubes, of which the following is a full and concise description.

My invention relates to safety devices for vacuum tubes, my more particular purpose being to protect the vacuuml tube from breakage or other injur due to the use of an electric discharge wit in the tube.

More particularly stated, my invention relates to safety devices for vacuum tubes of the type commonly employed in X-ray photography and iiuoroscopy and in whic an electric discharge takes` lace inside of a glass tube, under conditions such that zo some portion of the tube is likely to be broken by excessive heat from the cathode, or otherwise injured by continuous bombardment by cathode rays. By my invention I seek to avoid the difficulties just as mentioned.

An X-ray tube, as ordinarily constructed, comprises among other things a globular member of glass provided with a pair of glass necks integral with it and extending in opposite directions. One of these necks supports the anode and the other the cathode.

In the use of the tube, the neck supporting the cathode is exposed to danger of breaka e, owing to the excessive heat develope by the cathode rays. When a fracture occurs it usually takes place in the neck which houses thecathode, and in that portion of the neck where the cathode rays are 4o most activewhen in consequence there is excessive heating.

The danger of breaka e from the cause just stated is increased i the inner surface of the tube has become encrusted with metal,

deposited from metallic vapors formed from either the cathode or the anticathode.

Again, it often happens that the X-ray tube acts abnormally even when apparently uninjured, owing to conditions brought eo about by the action of the cathode rays, and

particularly to the presence of metallic deposits upon the internal surface of the neck in which the cathode is housed.

Heretofore in this art it has been customary to place a metallic shield,in the form of a cylinder, around the cathode in order to plrotect the glass neck in which the cathode is oused. vThis shield is designated as a cathode shield. It tends to protect the wall of the glass neck against bombardment by .cathode rays, and against leakage from the cathode to the glass neck. Sometimes this shield is placed in direct metallic contact with the cathode, yet not in direct contact with the glass neck. In some instances the 'shield is spaced about midway between the cathode'and the wall of the glass neck. In

other instances the shield is placed in con.

tact with the glass Wall of the neck.

With the shield arranged in either of the three ways just mentioned, however, a puncture ofthe glass wall of the neck is liable to occur at any moment while the tube is in use.

Not only that, but the cathode shield is also liable to be pierced by electric discharges taking place from the shield to the glass wall and such discharges are easily set up owing to the formation of I uetallic de osits produced within the tube.

ecause of the facts above stated the metal shield, if located as heretofore, does not afford adequate protection against breakage of the tube.

I have made this discovery, that by following certain principles hereinafter discussed, it is possible to determine for the shield a definite form and a relative position in which it can aiold adequate protection to the. tube.

I have ascertained from observation, based upon experiment, that the cathode shield must be so located as to intercept all cathode rays emanating from the sides and rear portion of the cathode, and also as far as possible all cathode rays tending to pass directly from the concave face of the cathode to the adjacent inner surface of the glass neck in which the cathode is located.

By making the cathode shield a little longer than usual, and projecting or extending it slightly past the concave end of the cathode, I indit practicable to cut 0H most of the cathode rays tending to pass from the concave face o cent inner surface of the glass neck; and thus it is practicable to prevent discharges :from` the edge of the cathode to the 'glass neck. i

I also makeprovision to prevent the cathode shield from accumulating an undue potential.

Reference vis made to the accompanying drawing forming a art of this specicationand in which li e reference characters indicate like Iparts in both of the figures.

Figure 1 is a side view, partly in side elevation and partly 'in section, of an X-ray tube equipped with my invention.

Figure 2 is an'enlarged central section through the cathode shield and parts immediately associated therewith.

A glass bulb 3 is rovided with two tubular necks 4, 5, ma e of lass and integral with the bulb. The nec s 4, 5, are designated respectively as the anode neck and the cathode neck.

The anode is shown at 6 and may be of the usual or any desired construction.

The cathode appears at 7 and is` made of suitable metal, preferably aluminum. It is provided with a cylindrical portion 7 of reduced diameter and with a concave face fb; also with a cupped edge 7c bounding this ace.

The cathode is secured upon a conductor 8, in the form of a metallic rod. This rod extends axially through a supporting tube 9 made of glass and carrying two annular 4members 10, 11 made also of glass, and disposed concentrically.

The general diameter of the portion 7 of the cathode is the same as the external diameter of the annular member 10.

Fitted partly upon the annular member 10 and partl upon the portion 7a of the. cathode is a s eeve 12, made of iron and having the general form of a hollow cylinder.

The cathode shield is shown at 14, and has a general cylindrical form. It is made of metal, preferably either steel, copper or aluminum, and is fitted upon the annular member 11, whereby it is supported. The cathode shieldis provided with a portion 14 of greater diameter than the portion in actual contact with the annular member 11.

A metallic tongue 15, of platinum, steel or any other appropriate metal is by means of rivets 16 mounted upon the inner surface of the cathode shield. This tongue extends into close proximity to the adjacent surface of the iron sleeve 12. An adjusting screw 17 extends loosely through a hole in the cathode shield and makes a working engagement with the tongue 15, through which it extends. By means of the screw 17, the tongue 15 is adjusted relatively to the iron sleeve 12.

the cathode to the adja 'though the cathode shield becomes electrically charged from the action of the cathode rays, it is repeatedly discharged, as any charge accumulating upon it passes from the free end of the tongue 15 to the iron sleeve 12, and thence to the cathode, during the intervals between the main discharges taking place through-the tube. Under no conditions, however, can any discharge take place from the cathode shield to the glass wall of the cathode-neck 5 even if the inner surface of the cathode neck be encrusted or frosted with metal. This is because the distance from the cathode shield to the nearest adjacent portion of the cathode neck is too great to lallow such discharge to take'place between the impulses. I find that the distance from the cathode shield to the nearest adjacent portion of the cathode neck should be at least three times the shortest distance between the cathode and cathode shield.

My arrangement of the arts as described accomplishes another goo purpose, in that it has a tendency to prevent the formation of excessive uantities of metallic vapors in the X-ray tu and also to prevent the accumulation of such vapors in that portion of the tube adjacent the concave Lace of the cathode.

Without the tongue 15 it would not be possible to prevent electric discharges from taking place from the cathode shield to the iron shield and thus to the cathode, under such conditions as to liberate metallic vapors in close proximity to the concave face of the cathode. Such vapors have a tendency to render the action of the tube anomalous of freakish, and are of course undesirable. By my arrangement, however, I reduce the production of the metallic vapors and prevent them from reaching the concave face of the cathode. In my construction and arrangement of the parts there is no tendency toward the formation of such vapors except at the pointwhere, small discharges take place from the tongue 15v to the adjacent surface of the iron sleeve 12, or in other words, within the cathode shield 14. The point where this takes place is cool and remote from the concave face of the cathode and in a region where the temperature is relatively low. The conditions surrounding the discharge in question are such that the vapors are condensed and thus prevented from getting into the main body of the ranged as to reduce, as far as practicable, the

tube; that is, into the bulb 3. In practice it is found that the metals of the vapors thus formed are forthwith, deposited upon the surface of the iron sleeve 12, in close proximit to the pointof the tongue 15. Thus the ormation of the vapors is localized, and the vapors are to all intents and urposes detroy'edas formed and thus ren ered harmess. v

The parts .are so proportioned and arnumber of cathode rays reaching the glass wall of the cathode neck 5 from the concave face 7b or from the cupped edge 7c or any rear portion of the cathode. f

I find in practice that if cathode rays pass directly and in straight lines from thev concave face 7 and from the cupped edge 7 to a portion of the cathode neck immediately adjacent, such portion is heated quite rapidly and to a high temperature, thus increasing the danger of breakage. I therefore place the cathode and the cathode shield in such positions relatively to the cathode neck 5 and to each other as to prevent as far as practicable this result. Following this idea, I place,` the cathode far enough to the left according to Figures 1 and 2 to leave the cupped edge 7 a little short of the left end of the cathode neck 5. In so doing I place the cathode shield so far to the left that its left end overlaps the adjacent cupped edge of the cathode to an extent sufficient to cut off most,` or at least a large proportion, of such rays from the concave face of the cathode as would otherwise fall upon the adjacent inner surface of the glass cathode neck.

The operation of my device is as follows:

vThe parts being` assembled and arranged as Shown in the drawing and as above described, the X-ray tube is mounted in position, andA electric discharges are sent through it in the usual or any desired manner so as to produce Roentgen or X-rays.

The cathode shield effectively protects the inner surface of the glass cathode neck from the cathode rays, and thus prevents overheating of the cathode neck and consequent breakage of the X-ray tube. The cathode shield, because of its position relatively to the cathode, serves to prevent the cathode rays Vfrom the concave face of the cathode and any rear portion thereof from reaching the adjacent encircling portion of the cathode neck, in suilicient quantities to overheat Such portion. Differences of po- ,tential developing between vthe cathode shield and the' cathode are neutralized by discharges which 'are localized as above described, and all metallic vapors generated by such discharges are condensed at a point remote from the bulb 3 of the X-ray tube, and thus are localized along with the discharges.

.thus protected from overheat-ing.

I claim:

1. In a safety device for X-ray tubes the combination, with an exhausted glass cathode neck and a cathode shield and cathode located within said cathode neck, of a discharge gap located within said exhausted cathode neck and provided with means for localizing, at a particular point, the discharges from sald cathode shield to said cathode.

2. In a safety device for vacuum tubes the combination, with a metallic cathode and anv evacuated hollow member enclosing said cathode, of a cathode shield having a portion extending directly between said cathode and an adjacent portion of said hollow member, and means for localizing the formation and condensation of metallic vapors within said hollow member.

3. In a device of the character described the combination of an exhausted vessel containing a cathode and a cathode shield, of means for localizing the formation of objectionable vapors within said exhausted vessel, in a predetermined region relatively to said cathode.

4. In a vacuum tube the combination, with an exhausted vessel, a cathode mounted therein and provided with a terminal face, and a cathode shield mounted within said exhausted vessel, of means located within said exhausted vessel for localizing the condensation of vapors in a portion of said exiausted vessel remote from said terminal ace.

5. In a vacuum tube the combination, with an exhausted vessel and a cathode and a cathode shield mounted within said ex. hausted vessel, of means for facilitating a discharge within said exhausted vessel, at a predetermined point between said cathode and said cathode shield.

6. In a vacuum tube the combination, with an exhausted vessel and a cathode and a cathode shield mounted therein, of a tongue made of conducting material and mounted upon said cathode shield, said tongue being located within said exhausted vessel and extending toward said cathode in order to facilitate discharges from said cathode shield to said cathode.`

lil

mediate said cathode face and the nearest adjacent portion of said cathode neck in order to screen said neck vfrom the cathode rays, and means for facilitating dischar es from the cathode shield to the cathode, t e space between the cathode shield and the neck being sufficient to prevent discharges taking place therebetween.

ARTHUR MUTsofmLLER. 

